The Collaborative International Dictionary of English v.0.48:

Altissimo \Al*tis"si*mo\, n. [It.; superl. of alto.] (Mus.)
   The part or notes situated above F in alt.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

high-pitched \high-pitched\ adj.
   1. high in pitch or frequency; -- used of sounds and voices.
      Opposite of low. [Narrower terms: adenoidal, pinched,
      nasal; altissimo; alto; countertenor, alto;
      falsetto; peaky, spiky; piping; shrill, sharp;
      screaky, screechy, squeaking, squeaky, squealing;
      soprano, treble; sopranino; tenor]

   Syn: high.
        [WordNet 1.5]

   2. set at a sharp or high angle or slant; as, a high-pitched
      roof.

   Syn: steeply pitched, steep.
        [WordNet 1.5] high-power

WordNet (r) 3.0 (2006):

altissimo
    adj 1: very high